Small Airway Dysfucntion in Severe Asthma: Impact on achieving Clinical Remission

Background: This study aimed to evaluate the impact of Small Airway Dysfunction (SAD) on achieving clinical remission in patients with severe asthma on biologic therapy. Methods: A prospective, observational study in 133 patients with severe asthma. SAD assessment was conducted using spirometry and impulse oscillometry (IOS). Clinical characteristics, biomarkers, gene polymorphism of IL-4 and IL-13, and asthma control parameters were collected before biologic initiation. SAD was defined as FEF50% < 60% predicted and R5-R20% ≥ 35%, and clinical remission (CR) was defined with the following; the absence of exacerbations and oral corticosteroids (OCS) use, an Asthma Control Test (ACT) score ≥ 20, an Asthma Control Questionnaire (ACQ-6) score ≤ 0.75, and a forced expiratory volume in one second (FEV1) ≥ 80% predicted after one year of continues use of biologic therapy. Results: SAD was present in 66.92% of severe asthmatic patients, based solely on impulse oscillometry, and 55.5% based on spirometry. The confirmed prevalence of SAD was 43.51% when both modalities were combined. Factors associated with SAD included older age group (p=0.001), allergic rhinitis (p=0.003), diabetes mellitus (p=0.02), and hypertension (p=0.02). However, IL-4 and IL-13 gene polymorphisms were not associated with SAD. Interestingly, SAD had a negative correlation with biomarkers like BEC (p=0.01). However, no significant correlation was observed with total IgE or FeNO. Overall CR in severe asthmatics was 17.29%. However, only 21% of patients with SAD achieved CR. Additionally, SAD had a significant negative effect on ACT and ACQ scores. Conclusion: SAD is prevalent in severe asthma and negatively influence the liklihood of CR.